# Empty tags in <msup> cause strange behaviour

RESOLVED FIXED

Core
MathML
P3
normal
RESOLVED FIXED
19 years ago
18 years ago

Trunk
---
x86
Linux
Points:
---

## Attachments

### (1 attachment)

 871 bytes, text/plain Details
(Reporter)

### Description

19 years ago
<msub> and <msup> each take two parameters (base and sub/super script).
If the base is empty for <msub> then it behaves as I would expect - like latex's
${}_n$.
But if the base is empty for <msup> nothing is displayed - unlike latex's
${}^n$.
(See the url or attached file for a clear example.)

From the point of view of tex to mathml convertors it would be preferable if
empty tags were accepted and displayed in a tex like way.
(Reporter)

### Comment 1

19 years ago
Created attachment 5694 [details]
test file
(Reporter)

### Comment 2

19 years ago
Any news on this bug? Are there problems confirming  it? Or have better things

to do!


(Assignee)

### Comment 3

19 years ago
Saw the problem. Accepting bug.

It is necessary to know the height that should be given to the empty element.
For TeX, the base in ${}^n$ a zero-width box, and the height is non-null
(this way, the sub/super script can be shifted w.r.t. that height)

Do you know what should be the height of ${}$?

Status: UNCONFIRMED → ASSIGNED
Ever confirmed: true
(Reporter)

### Comment 4

19 years ago
I asked David Carlisle what (la)tex does about ${}^x$. Here is his reply:

> For TeX, the base in ${}^n$ a zero-width box, and the height is non-null

>(this way, the sub/super script can be shifted w.r.t. that height)

>Do you know what should be the height of ${}$?

well the height of the box made by  ${}$ is zero, which I suppose isn't

In fact the superscript gets raised by virtue of

\rule 18a. If the translation of the nucleus is a character box, possibly

followed by a kern, set $u$ and~$v$ equal to zero; otherwise set

$u\leftarrow h-q$ and $v\leftarrow d+r$, where $h$ and~$d$ are the height

and depth of the translated nucleus, and where $q$ and~$r$ are the values

of $\sigma_{18}$ and $\sigma_{19}$ in the font corresponding to styles

$C\mathord\uparrow$ and~$C\mathord\downarrow$.  \ (The quantities $u$

and~$v$ represent minimum amounts by which the superscript and subscript

will be shifted up and down; these preliminary values of $u$ and~$v$ may

be increased later.)

ie font parameters 18 and 19 effectively force a minimum shift.

I am not sure of the current state of the sub project to instill

these rules from appendix G into mozilla, in the particular case of

wanting to know what to do about {}^x I'd just use the x height of the

current font. ie raise it as if it was x^x.


(Reporter)

### Comment 5

18 years ago
Fixed I believe. Status to resolved' ?

(Assignee)

### Comment 6

18 years ago
Resolving as FIXED.`
Status: ASSIGNED → RESOLVED
Last Resolved: 18 years ago
Resolution: --- → FIXED
You need to log in before you can comment on or make changes to this bug.